As a fluid pressure actuator, there has been known the one obtained by covering the outer periphery of a rubber tube (inner tube) with a mesh-like covering material (mesh sleeve) made of a resin without expanding/contracting property. The diameter of the mesh sleeve increases when the inner tube is expanded by feeding the air into the inner tube of the fluid pressure actuator. An increase in the diameter of the mesh sleeve is converted into a decrease in the length of the actuator since the material of the mesh sleeve has no expanding/contracting property. A contracting force (driving force) is obtained accompanying the decrease in the length of the actuator.
The fluid pressure actuator constituted chiefly by the elements of the mesh sleeve made of a resin and the inner tube made of rubber has a feature in that it is much lighter than the air cylinder equipped with a metallic cylinder and a rod. It is, therefore, expected that the fluid pressure actuator can be applied in a wide field of technology where the above-mentioned feature is required.
As the use of the fluid pressure actuator, there can be exemplified an artificial muscle or rehabilitation equipment for physically handicapped persons. Among them, the rehabilitation equipment for the physically handicapped persons may be the ones for the joints of the upper and lower limbs that have withered after the therapy for extended periods of time.
The conventional rehabilitation equipment for the joints, for example, the rehabilitation equipment disclosed in, for example, JP-A-2000-051297 is using an actuator such as a motor. However, since the motor is incorporated as a drive source in the equipment, the rehabilitation equipment becomes bulky and heavy. This involves a problem from such a standpoint that the handicapped person must carry and operate the rehabilitation equipment. It has, therefore, been desired to apply an air pressure actuator to the rehabilitation equipment for the physically handicapped persons.
As a result of experiment conducted by the present inventors, however, it was learned that when the above conventional fluid pressure actuator is repetitively expanded and contracted, for example, several hundreds of times, the inner tube expanded by the fluid (air) that is supplied partly swells through the mesh of the mesh sleeve often causing the inner tube to be damaged. Further, when the above fluid pressure actuator is repetitively used, the inner tube is often damaged or the mesh-like fiber of the mesh sleeve is broken.
U.S. Pat. No. 4,733,603 (hereinafter referred to as prior art document 1) and JP-A-61-236905 (hereinafter referred to as prior art document 2) are disclosing technical ideas for preventing the breakage of the fluid pressure actuator and for elongating the service life thereof. In order to decrease the friction between the inner tube and the mesh sleeve in the fluid pressure actuator, the prior art literature 1 discloses an art for forming a mesh sleeve by burying a mesh-like covering material in a layer of a soft material having expanding property and by providing a perforated friction-lowering layer between the inner tube and the laminar mesh sleeve. The above prior document discloses that the friction-lowering layer decreases the resistance at the time of expansion produced by the friction between the tube and the laminar mesh sleeve.
According to the fluid pressure actuator disclosed in the above prior document, however, the mesh sleeve must be produced by burying the mesh-like material in the layer of the soft material and, besides, the inner tube must be covered with a perforated friction-lowering layer leaving problems that must be solved, such as complex structure and increased cost.
The prior art document 2 is disclosing the art in which the mesh sleeve is covered with a rubbery elastic covering member which is introduced into gaps of mesh of the mesh sleeve.
According to the art disclosed in the above prior art document 2, however, a parting agent is simply applied between the mesh sleeve constituted as described above and the inner tube. It is therefore presumed that the inner tube is broken within short periods of time due to the friction between the inner tube and the mesh sleeve leaving a problem that must be solved, i.e., extend the service life of the fluid pressure actuator.
It is a first object of the present invention to provide a fluid pressure actuator which is simple in the structure and has a long operation life.
It is a second object of the present invention to provide a CPM device using the fluid pressure actuator of the present invention, i.e., to provide a CPM device for rehabilitation for the physically handicapped persons suffering from acquired disorder in the limbs or in some of the limbs.